B. Riccardi et al./ Fusion Engineering and Design 51-52(2000)11-22 (M P a) Fig 3. Stress displacement curve at RT and 800C for neutron irradiated Sic/SiC composites tion temperature [14]. The average strength of the Sic matrix was observed with the formation of SiC SiC composites in the 'as received condi- enlarged tube-like channels surrounding the tions, measured by a three-point flexural test, was fibres. It has been shown that the linear expansion 305 MPa without significant temperatur of the matrix is poorly prevented by the fibre: in dence. The mechanical response of irradiated ma ruIc ular for 1. 29 dpa the expansion dose deper terials showed a progressive strength degradation dence is below the saturation values and for 2.69 with increasing damage dose. The strength values 5.23 dpa is similar to those of monolithic SiC with partially recovered for tests carried out at a high fibre-matrix mismatches being observed since low temperature(800oC)for all the neutron doses. fluences. The fibre frictional work against the The composites submitted to higher neutron ex- matrix seems to be effective at low doses (1. 29 posures exhibited a brittle behaviour (sharp load dpa); but at higher dose(2.69, 5.23 dpa), the large drop following the point of maximum strength) fibre/matrix detachment makes the fibre frictional with a slight recovery of the elastic modulus(Fig. work rather ineffective and, consequently, deter- 3), which represents the main limitation for the mines a dramatic reduction of the toughness of irradiation response for these materials. At low these composites damage doses (1.29 dpa)an improvement of In parallel with neutron irradiation helium im- toughness was observed but at higher damage plantation campaigns were also carried out at the doses (i.e. 2.69 and 5.23 dpa) both the strength IAM-Ispra cyclotron [15]. The implantation was and the toughness are significantly reduced. The performed at 950oC and helium concentrations up reasons for this decrease became apparent from to 2500 appm where obtained. The mechanical composites morphology and dimensional changes response of the helium implanted composites was induced by the irradiation. The NICALONTM CG evaluated with a post irradiation flexural test car fibres shrank due to the presence of an oxygen ried out at Rt. The results showed a mean 38% rich glassy phase whilst a linear expansion of the decrease of strength and the stress displacement16 B. Riccardi et al. / Fusion Engineering and Design 51–52 (2000) 11–22 Fig. 3. Stress displacement curve at RT and 800°C for neutron irradiated SiC/SiC composites. tion temperature [14]. The average strength of the SiCf /SiC composites in the ‘as received’ condi￾tions, measured by a three-point flexural test, was 305 MPa without significant temperature depen￾dence. The mechanical response of irradiated ma￾terials showed a progressive strength degradation with increasing damage dose. The strength values partially recovered for tests carried out at a high￾temperature (800°C) for all the neutron doses. The composites submitted to higher neutron ex￾posures exhibited a brittle behaviour (sharp load drop following the point of maximum strength) with a slight recovery of the elastic modulus (Fig. 3), which represents the main limitation for the irradiation response for these materials. At low damage doses (1.29 dpa) an improvement of toughness was observed but at higher damage doses (i.e. 2.69 and 5.23 dpa) both the strength and the toughness are significantly reduced. The reasons for this decrease became apparent from composites morphology and dimensional changes induced by the irradiation. The NICALON™ CG fibres shrank due to the presence of an oxygen rich glassy phase whilst a linear expansion of the SiC matrix was observed with the formation of enlarged tube-like channels surrounding the fibres. It has been shown that the linear expansion of the matrix is poorly prevented by the fibre: in particular for 1.29 dpa the expansion dose depen￾dence is below the saturation values and for 2.69/ 5.23 dpa is similar to those of monolithic SiC with fibre-matrix mismatches being observed since low fluences. The fibre frictional work against the matrix seems to be effective at low doses (1.29 dpa); but at higher dose (2.69, 5.23 dpa), the large fibre/matrix detachment makes the fibre frictional work rather ineffective and, consequently, deter￾mines a dramatic reduction of the toughness of these composites. In parallel with neutron irradiation helium im￾plantation campaigns were also carried out at the IAM-Ispra cyclotron [15]. The implantation was performed at 950°C and helium concentrations up to 2500 appm where obtained. The mechanical response of the helium implanted composites was evaluated with a post irradiation flexural test car￾ried out at RT. The results showed a mean 38% decrease of strength and the stress displacement